What is the universe mostly made of?

WE WERE PACKED IN TIGHT: a team of some 30 physicists, engineers, biologists, and–mostly–miners. Ex-miners, really. This hadn’t been an active mine for 18 decades. The guy working the lift allow the winch operator know that the taxi was complete, that we were a go. Somewhere overhead, the more frigid South Dakota winds whistled faintly, whipping throughout the Black Hills on this February day. A reminder of what, the whole world we were departing, as we started to drop.
And drop. And drop.
The cage proceeded gradually and steadily, covering roughly five feet a second. We passed openings to shallower flooring, dark and halfway with water. Biologists worked some of these, scraping up bacteria from the muck, analyzing extremophiles to contemplate life-forms which may exist on different planets. An epic puzzle, sure, however, our des- tination was further below: floor 4850 from the former Homestake Mine in Lead, out of Deadwood, South Dakota, now the San- ford Underground Research Facility, or SURF. Here physicists from all over the world are attempting to solve a puzzle more fundamen- tal than existence itself. Namely, what is the universe mostly made of?

Atank filled with xenon awaits transportto its home in a formergold mine below Lead, South Dakota.

Protons, neutrons, electrons–those are all familiar to people. Ele- mentary, also. We also have accounted for its weirder, smaller, subatomic material: both the alpha and beta particles, the quarks, the neutrinos. Still, they don’t add up. Not by a very long shot. For presence , well, exist, such as galaxies to spin how they do, to get light from distant stars to flex how it seems , there must be quite a little more out there than we’ve seen so far. Even the Stan- dard Model, that classifies all basic particles, accounts for just 16 percent of the universe’s mass. That leaves a second 84 percent. There are lots of theories about what this rest might be, but all of it goes by precisely the exact same name: dark matter. It may be something, one type of particle, sort of similar to a proton; or it could be several different things, such as an electron and also a quark. Until we have discovered tangible evidence, we will not really know for sure. The Objective of the elaborate experiment
This cage was descending toward is to find that proof. In the profound, tucked away in the humming in- terference radiating from all around ussits a wildly intricate detector–let us call it a camera trap. It was designed and constructed to record the presence of the lead contender for dark thing, a physics unicorn called a WIMP, for weakly interacting gigantic particle. The project includes in its center a five-foot-tall tank full of about one-quarter of this planet’s annual sup- ply of liquid effluent. When the installation comes online–when overdue 2020–it will operate for five decades. At that point the team could have either found evidence of a par- ticle that may be dark subject, or. . .not. The project is referred to as LUX-ZEPLIN, or LZ. LUX stands for Large Underground Xenon, ZEPLIN for ZonEd Proportional scintillation from LIquid Noble gases. It may well be our
Best shot yet at spotting a WIMP.

Mine carts transport new kinds ofworkers and equipment.

“This is the most enjoyable time for math, because we still have the really big mysteries in front of us,” states Kevin Lesko, a senior physicist at the Lawrence Berkeley National Laboratory, who coordinates the LZ project. In early 2020, the detector was in the last throes of assembly. Teams of six to 12 physicists and engineers worked in two changes each and every day, from 8 a.m. to midnight, on a experiment that over five years has demanded specialists in fields as varied as photon detection and computer modeling, and even out of some 37 institutions across seven nations. “Folks prefer to say we understand how to describe the universe. And now we are attempting to figure out the big map of the universe,” Lesko says of this enormous collective effort.
The xenon tank is the crucial instrument for satisfying in that map by determining what most matter may be. Back in October 2019, it flew down the shaft via the cage at a highly orchestrated daylong event that left little room for error or jostling. A single slide and wreck, years of planning, and millions of dollars in research and de- velopment, could have gone down the mine shaft.

THE EVIDENCE OF DARK thing is every- where, Though we have yet to peek the
Substance .
Velocities of galaxy clusters appeared to make absolutely no sense: The gravitational forces of visible matter would not be sufficient to keep the groupings from scattering. For all those celestial bodies to congregate the way they do, a few un- seen mass (and gravity) has to be helping pull them collectively. In the 1970s, astronomers Vera Rubin and Kent Ford were studying that the blessings of the Andromeda galaxy and found, to everybody’s astonishment, that the stars in the outermost borders moved just as quickly as people at the middle, surpassing Kepler’s third law of planetary (in this scenario, galactic) rotation, which maintains that the ob- jects revolving round a center should proceed more gradually as the distance from the middle increases. They do not suggests that some farther-away mass influences these bodies. There are different hints on the market, such as how light from remote celebrities bends its journey to us, and the consequences of the cosmic microwave back- ground, as well as also the elliptical and spiraling shapes of galaxies. All of this points to the presence of a excellent, nonluminous, hidden mass.
Peering out to area gives us a sense of the effect black mat- ter has on the shape and look of our universe, but all that proof is indirect, a shadow of a shadow. This imperceptible material will stay a puzzle until physicists could observe the particle or particles which accounts for this, which they’ve been attempting to do for around 30 decades. Some experiments attempt to plot a chart that points into dark matter by searching out signs of its corrosion through high-flying tools such as the Fermi Gamma-ray Space Telescope. They call this tactic indirect detection.
Other techniques instead try to create dark matter. Considering that 2012, physicists are running experiments that could do exactly that–on the Large Hadron Collider particle accelerator at CERN, near Geneva, Switzerland. The attempts, jointly called ATLAS, smash together protons to mimic the conditions of the big bang, when everything in our world formed, for example, theoreti- cally, dark matter. By comparing the energy that they understand went into the accelerator together with the dimensions of what comes out, the scientists could prove its presence.
More frequently, dark thing sleuths want hard proof. That is, they would like to immediately detect it. But again, no one is precisely sure exactly what it is they’re looking for. Aside from the WIMP, there is another potential offender: a the- oretical particle called an axion. If they exist, then axions would help clarify just how neutrons, even people with charged quarks kicking around inside them, be able to stay impartial. They’d also be approximately one trillion times less massive than an electron, so which means trillions would fit in a space the size of a sugar cube. Physicists think the trick to sending them will be speeding up their otherwise glacial decay into photons, which are rather simple to see. A sensor constructed by a team at the University of Washington wields an enormous and incredibly strong mag- net to hasten that speed, even though a resonator tuned to the microwave frequency of the potential decay keeps watch.
Nevertheless amid the broad field of dark thing makeups which

Scientists have drifted over the years– such as applicants out of primordial black holes to MACHOs (massive astro- physiological compact halo objects) half of the majority of our sunshine –WIMPs have re- mained a key goal. If they are out there, they’d neatly align with some other popular notion in theoreti- cal physics called supersymmetry, the idea that for every piece of mass we can observe there’s also a counterpart that is not luminous, the yin to its yang. If that idea’s correct, what we’ve added up from what cov- ered from the Standard Model will be reflected by the WIMP presence. The world, unknowable and chaotic as it may look, tends toward tasteful solutions such as this one. Or elegant solutions such as this one have a tendency to explain the universe.
Nevertheless, even on the planet of WIMPs, questions remain. The particles may exist in a range of masses, by about one pro- ton into 100,000 protons. 1 experiment, called SuperCDMS, is looking for wee-er WIMPs than the LZ. Based in a nickel mine in Ontario, Canada, it depends upon six sensors made of sili- scam or germanium crystals; when a WIMP hits one and interrupts a crystal’s electrons, the interaction will produce vibrations, a signal that can be amplified. The rig operates –450°F to cut out the noise generated by renewable energy. Plus in addition, it sits deep underground–6,800 ft –protected from the radioactivity of daily lifetime, the cosmic buzz coming away everything from stars to the bottoms of your Chuck Taylors.
There’s another xenon-based WIMP detection effort, an worldwide effort located under Italy’s Gran Sasso hill –also aptly called XENON. The scientists – volved declared in June 2020 their experimentation was registering extra background signals, which could end up demonstrating there are axions. Or it may be neu- trinos. Or the result of contamination. Much like much in dark matter, the information can seem to be on the edge of reality-shifting, but turn out to be nothing in any way.
Lesko, who has been working on such undercover experiments–such as the LZ’s younger Testament, LUX–for the better part of 30 years, explains why these attempts always occur so deep underground. You do it at the middle of new york, you are not going to listen to it, there is simply too much noise. You would like to escape from our backgrounds–both the cosmic rays and crap we’re bombarded by would hide the very rare signs we’re searching for.” But here Lesko stops himselfThe sign the particle,”isn’t always rare, what is rare is the in- teractions using items that we can observe.” That’s why, if Lesko would venture out to Fight (pre- pandemic, obviously ) to pay a visit to the mine-turned-lab for a week each month, a great deal of what he along with the crews would operate on was keeping absolutely everything as exception- ally fresh as you can. It’s a challenging task anywhere, but it’s absurdly so way down within a tunnel carved into the stone.
And all of us marched out. Crews of scientists and
Staff piled into electrified packs –mine ! — to travel a quarter-mile-long, unlit, dirt-floored passageway toward more distant labs. Closer to where the lift had delivered , I exchanged my own boots for a set of quite clean street runners which never left this space. I wiped down my telephone, pen, laptop, and hands and stepped across a sticky floor to eliminate any dust from the shoes, then down a long hallway that led to the room where the LZ was arriving together. Throughout the doors came a lengthy, large whistle that seemed like a dreadful scream.
“That’s the liquid we’re running through the plumbing –it’s loud!” Manalaysay was down here with a crew of graduate students, working over a few months to complete assembling all of LZ’s thousands of constituent parts, which ended almost all the room.
If the screaming died down, we walked through a pair of double doors and into the distance. I expected first to see the tank at the middle of this LZ experiment, spacious and gleaming. Rather you will find rows of wires and pipes running from sensors to stacks of computers beyond the container; a cryogenics panel for cooling the xenon gas into only beneath –163°F (the temperature where it liquefies) and helping to lower background interference within the tank itself; vinyl curtains draped around areas still undergoing meeting; air ducts and lockers and orange robes and warning signs. This could be filled with 70,000 gallons of water to further buffer the interior xenon chamber–in a feeling, a colossal thermos. Why xenon? It’s extremely dense and, as one of those noble gases, it is inert. Most of the time, it does not react to many things it comes into contact . It is, in other words, extremely silent. So responses inside the element tend to be noticed, which is precisely what you need when attempting to see a sudden flash that may wind up demonstrating the existence of dark matter. Inside this titanium vessel were photon sensors –that the”cameras” in the snare: a few hundred 3-inch-wide tubes honeycombed into two nearly 5-foot-diameter circles at the top and bottom of the massive canister.
We resigned from the porthole and scaled a ladder into a mezzanine level midway the outside tank, at which Theresa Fruth, a physics researcher fellow in Uni- versity College London, was working on the sensors. She was testing how they would function inside the remainder of the system. The tubes act as catch and amplifica- tion devices, ” she clarified. If a particle, then WIMP or differently, moves through the tank and then strikes the nucleus of a xenon atom, the result is power, in the Shape of light: The arrays absorb those and convert them into electrons. Each one represents a data point–Y, X, and Z coordinates–that shows where
In the field an interaction is coming from.
The huge bulk of the events will stem from the de- cay in the surrounding stone walls. “This will happen,” Fruth said. “We don’t care” Physicists know what those signs look like and can easily dismiss them. Besides, among the advantages of owning such a enormous amount of xe- noninvasive, ” she explained, is its outer borders –in addition to the tank , along with the water, and another tank, and the mile of earth above–act as a buffer. “When we proceed nearer to the middle, we get much more silent.” This is the spot where they may find dark matter. Or at which”we could reasonably search for a rare discussion .”
ARARE INTERAC TION, WERE this to happen in-
Side the tankcould blip without anybody even noticing. The last trick, perhaps the trickiestof all, would be to make certain that we do spot this particular flash of action involving all of the others. Once the LZ comes online, it will register approximately a billion interactions per year. This petabyte value of data is the responsibility of Maria Elena Monzani. She works at the SLAC National Accelerator Laboratory at Stanford and manages the software and computing infrastructure of LUX-ZEPLIN. Because no one has seen a dark thing interaction be- finished, it is important to attempt to be sure about what we’ve actually seen. Monzani coordinates the cataloging and modeling of the”knowns” so as to make it eas- ier for the unknowns to stand outside. “We’re likely to have a couple billion events, and dark matter is going to be a few,” Monzani says. “It is very important we know what those few billion events are. As Soon as You know that, then
It is possible to know,’Ah, that is not something. ”’
Monzani manages what is, in essence, an inoculation against the mind’s urge to observe matters (patterns, parti- cles) which aren’t actually there. She has many platoons’ value of physicists spread round the globe, working on two information centers running full simulations of their LZ. They’re calibrating the machine, the algorithms, and also , yes, the people. To calibrate a individual, Monzani and her team churn out datasets out of a simulation of their LZ tank, then, diabolically, insert extra data that looks just like the real thing–a procedure called salting.
Monzani’s crew drops in data that, say, looks like the energy that a WIMP would leave in its aftermath. They know these markers are fake, however their analysts do not, thus creating a blind test to reduce the bias that may come around from physicists’ really real desire to obtain an exciting interaction. After the trial run has been completed, Monzani’s team reveals which of these signals were placebos. What’s left is, in this case, the”real” ones produced by the LZ simulation (they’ll re- peat the procedure once the experimentation turns on and reside data starts coming ). Everybody wishes to discover black mat- ter. Salting pushes them to be honest.
Tems became the bulk of the campaign in midspring. In March 2020, the COVID-19 outbreak forced the fa- cility to shut down onsite work aside from critical maintenance. Some of the scientists remained in town, since traveling — particularly internationally–appeared dicey, and Lead (population 3,021) was still a pleasant enough place to be stranded for however long they would hang in this virus-induced limbo.
There is still plenty to do over – ground, lots of calibrations to perfect. No matter when they begin, it will take five decades of WIMP sniffing to collect enough information to understand if the particle is in the LZ’s detection array. And moreover, as project manager Lesko points out, those months of dual shifts had paid off: They’d nearly completed assembly down 4850, and the job was in a stable and safe spot. Few areas are more se- heal during a pandemic than one near a distance underground.
However, like the rest of us, they wonder when this all might be when they can become completely back to the experiment, and if, once they dowith all the LZ tank sealed along with detector arrays watchfully waitingthey’ll find anything whatsoever. Nevertheless team members such as Fruth, the photon sensor specialist, are sanguine about the chance of their lifetime’s work nothing. “Knowing that it’s not something is still worth something,” she states. When you aren’t certain exactly what a WIMP is, there’s worth in finding out what it is not.
Living with uncertainty and pon- dering that the anonymous is a comfortable space for these to maintain, because that’s what scientists do–especially physicists on this distinct ongoing search. “We draw on the line,” she says,”and we all say,’Look, we And then we push a bit further, and understand a bit more. And the line goes, and we proceed with it.”

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